This invention relates to control systems for an internal combustion engine, and more particularly to the measurement of exhaust gas temperature and the control of a heater of an exhaust gas oxygen sensor for an internal combustion engine.
There are many strategies for controlling the air-to-fuel ratio (A/F ratio) of an internal combustion engine. One approach measures the concentration of oxygen in the exhaust gas. A controller uses the oxygen concentration to control the A/F ratio. An oxygen sensor is used to sense the concentration of oxygen in the exhaust gas. The oxygen sensor must be operated within a specific temperature range to accurately sense the concentration of oxygen in the exhaust. Typically, the oxygen sensor must be operated between 650 and 850xc2x0 C. to provide accurate results. Until the sensor reaches the operating temperature range, the output of the oxygen sensor cannot be used to control the A/F ratio. A heater is used to raise and maintain the temperature of the oxygen sensor within the operating temperature range. If current continues to flow through the heater after the oxygen sensor reaches the operating temperature range and the exhaust temperature is high, the heater overheats and may be damaged.
Monitoring exhaust gas temperature is also important for emissions control. The level of emissions processed by the catalytic converter is dependent upon the temperature of the catalyst. The temperature of the catalyst, in turn, depends on the exhaust gas temperature. The exhaust gas temperature must be monitored to prevent the catalytic converter from overheating. Usually, the exhaust gas temperature is measured using a sensor or is calculated from the operating conditions of the engine. The use of a temperature sensor is more accurate but generally costs more than using estimation techniques.
In a vehicle including an engine, an exhaust, and an exhaust gas oxygen sensor with a sensor heater, a system according to the present invention estimates exhaust gas temperature. The system includes a first sensor that measures heater current though the heater. A second sensor measures a first engine operating parameter. A controller communicates with the first and second sensors and calculates an exhaust gas temperature value using a Kalman filter.
In other features of the invention, the Kalman filter receives the first engine operating parameter and the heater current as inputs. The second sensor is a mass flow rate sensor and the first engine operating parameter is a mass flow rate of the exhaust gas.
In yet other features, the controller maintains a temperature of the heater within an operating temperature range. A voltage sensor generates a sensor voltage signal based on voltage across the exhaust gas oxygen sensor. The controller calculates current through the heater based upon the sensor voltage signal and a sensor resistance. The controller calculates total resistance based upon the current through the heater and a voltage drop across the heater. The controller calculates a resistance of the heater based on a difference between the total resistance and the sensor resistance. The controller calculates a temperature of the heater based on the heater resistance. The controller calculates an error signal based on a difference between the heater temperature and the operating temperature range and varies a temperature of the heater based on the error signal. The controller generates an estimate of oxygen concentration in the emissions.
In other features of the invention, the exhaust gas temperature is used to control at least one of engine diagnostics and engine control.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.